Charakter skin swap

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Hi,
first of all, i could understand if you don´t want to help me cause i´m a leecher.

Now may question, pls someone eyplain me how to change the skins of characters.
I´ve got MyWarcraftStudio, GitchysMES , and BLP2PNG.
I changed my Draenei to an Undead, but he is blue >.< I´m not able to fix this, i tried soo much.

Pls help me!

(I searched around but didn´t find anything like this)
(sry for bad english, and sry it should be a Question not a request)